Keeping a Mandarin with the hopes of buying copepods to feed it is very admirable, but I'm afraid it's not the answer.
If your tank is not very mature, doesn't have an adaquate population of pods, and the fish will not take to any other food, then I regret to say it will starve and die.
The fact that you asked this question tells me that you care for this fish, and don't want to see it starve.
I suggest either finding this fish another home more suited to it's dietary needs, or returning it wherever you bought it - and maybe try again later with a larger tank dedicated soly for this species.
These are very difficult fish to keep for any real length of time, and can easily wipe out what you may think is tank rich in copepods.
Others have been successful, and they will tell you why and how.
I speak from experience
![Frown :( :(](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)